Abstract: Microplastic pollution is widespread worldwide and can enter organisms by ingestion or inhalation.In this study,an experimental group (with microplastics) and a control group (no microplastics detected) were set up,and a non-targeted metabolomic analysis was performed on K.pelamis muscle tissue from the Eastern Pacific Ocean using liquid chromatography-mass spectrometry to investigate the potential effects of microplastic contamination on their metabolites.The results showed that a total of 34 metabolites were significantly different,of which 19 differential metabolites were up-regulated and 15 differential metabolites were down-regulated.The differential metabolite analysis showed that methylmalonic acid and propionic acid were up-regulated to induce neurological disorders and may be responsible for the abnormal swimming pattern of K.pelamis.The metabolite content of 20-hydroxyarachidonic acid in the metabolites of K.pelamis muscle tissue was significantly upregulated (P=0.003) and the difference multiplier was 6.002-folds.Arachidonic acid metabolism was closely related to hepatic disorders of glycolipid metabolism and its abnormal metabolism may affect disorders of glycolipid metabolism.Malic acid downregulation might put K.pelamis at risk of bacterial infection.In contrast,glycerol-3-phosphate,creatine phosphate and hydroxy cumene glycosides were up-regulated as a self-protective mechanism for K.pelamis in response to microplastic accumulation.Metabolic pathway enrichment analysis showed that different metabolites were mainly enriched in metabolism,bile secretion,propionate metabolism,proximal tubular bicarbonate recycling,ethylbenzene degradation,glycerophospholipid metabolism,and cholesterol metabolism.Among them,cholesterol metabolism and glycerophospholipid metabolism were involved in building biofilms and maintaining the basic life activities of the organism;while ethylbenzene degradation and propionate metabolism were used to alleviate toxicity in vivo;and proximal tubular bicarbonate recycling was responsible for mediating blood pH.The results of the study provided some reference significance for the toxicology of microplastic pollution on marine fish.